Efforts for the coming year will be divided between two major projects: a) Identification and characterization of specific rete testis fluid and cauda epididymal fluid constituents which affect the metabolism, survival and motility of cauda epididymal, ejaculated and testicular spermatozoa. A major part of this project will be the identification of constituents in cauda epididymal fluid which are known to maintain a high sperm motility for long periods of time and which provides the most favorable environment for survival of testicular spermatozoa in vitro. b) The use of our model for serial collection of testicular lymph from conscious rams to study the mode of action of specific synthetic agents which interfere with normal Leydig cell function. The "drugs" will be injected either before or at the same time as ovine LH which is known to stimulate testosterone secretion by the Leydig cells. The sensitivity of our model and its rapid response to gonadotropic hormones will make it an ideal tool for testing agents that suppress testosterone secretion by the testis.